Marshall is a labor attorney based in Minneapolis. He has represented labor unions at the local and national level. He has also represented individual athletes, coaches, and administrative personnel at the amateur, collegiate and professional levels. Marshall is also a well-known newspaper columnist with the Star Tribune newspaper, MinnPost, Bench and Bar Magazine of Minnesota, Finance & Commerce newspapers, Sun Post Weekly newspaper chain, National Law Journal and others. In this role, he has written extensively about the possibility of college football players unionizing.

Marshall was born and raised in Minneapolis. He graduated from the University of Minnesota, Phi Beta Kappa with a degree in journalism. He also holds a J.D. from Stanford Law School, order of coif. In 2019 he was named Minnesota Attorney of the Year by Minnesota Lawyer magazine.